It is known that photographic images having a very high contrast can be formed using a certain kind of silver halide and such a photographic image-forming process has been used in the field of photomechanical process.
For example, it is known that line images or dot images having a high contrast and a high blackened density, wherein imaged portions are clearly distinguished from non-imaged portions, are obtained by processing a lith-type silver halide photographic material containing silver chlorobromide (having a content of silver chloride of at least 50%) with a hydroquinone developer having a very lowered effective concentration (usually lower than 0.1 mol/liter) of sulfite ions. However, in the process, the developer is very unstable to air oxidation since the sulfite concentration in the developer is low and thus various efforts and attempts have been made for keeping stably the activity of the developer.
Thus, to solve the problem of instability of image forming by the aforesaid development process (i.e., lith development system), an image-forming system capable of giving very high contrast photographic characteristics by developing using a developer having a good storage stability has been desired and systems of forming a super high contrast negative photographic images having a .gamma. (gamma) value of over 10 by processing surface latent image-type silver halide photographic materials containing specific acylhydrazine compounds with a developer having a pH of from 11.0 to 12.3, containing at least 0.15 mol/liter of a sulfite preservative, and having good storage stability are proposed in, e.g., U.S. Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606, 4,311,781, 4,269,929, and 4,650,746. These new image-forming systems have a feature that even silver iodobromide or silver chloroiodobromide can be used in the system while in conventional super high contrast image-forming systems, only silver chlorobromide having a high silver chloride content can be used.
However, since in the process of using hydrazine derivatives, the pH of the developer is higher than that of an ordinary lith developer, there is a problem that the pH value is liable to deviate and the deviation of the pH value is liable to cause inconsistency in the result of photographic characteristics.
For solving the problem, U.S. Pat. No. 4,269,929 describes that the sensitizing and contrast increasing effects of hydrazine derivatives by a developer having a lower pH value are realized by adding an amino compound to an alkaline developer using a dihydroxybenzene developing agent and a 3-pyrazolidone developing agent as the developing agents to increase the activity of the developer.
However, even by the aforesaid means, it is impossible to reduce the pH value to such an extent of not causing the deviation under the ordinary storage or conditions for use.
Also, an amino compound functions as a solvent for silver halide (see, C. E. K. Mees, The Theory of the Photographic Process,3rd Ed., page 370, and L. F. A. Mason, Photographic Processing Chemistry, page 43).
Thus, in the development process using a large amount of amino compound described in the aforesaid U.S. patent, a problem called as "silver stain" in the field of art is liable to occur. The silver stain means a fault that when in, for example, a process of processing a silver halide photographic material by an automatic processor and supplying a replenisher for the developer to the developer tank depending on the area of the photographic film processed, if the aforesaid developer is used for a long period of time, the silver halide eluted out from the photographic film processed deposits and attaches to the tank wall and rollers for conveying the film in the automatic processor as silver and the silver is transferred onto other photographic film to be separately processed.
For solving the problem of the silver stain, it is required to use a compound which has a function of increasing contrast and functions as a solvent for silver halide but no proper compounds from such a viewpoint have been known.